Catalyst for ammoxidation of paraffins

ABSTRACT

Ammoxidation of C 3  to C 5  acyclic alkanes with NH 3  and O 2  using (1) a mole ratio of alkane:NH 3  in the range from 2 to 16 and a mole ratio of alkane:O 2  in the range 1 to 10 and (2) a mixture of particulate catalyst compositions, the first being especially effective to promote formation of an unsaturated nitrile and an olefin from the paraffin, and the second catalyst composition being especially effective to promote the conversion of the olefin to the unsaturated nitrile. Catalytic compositions useful in the process are disclosed.

This invention relates to an improved process for the catalyticammoxidation of paraffins containing from 3 to 5 carbon atoms toα,β-unsaturated nitriles, especially paraffins containing 3 to 4 carbonatoms. Most important is the ammoxidation of isobutane tomethacrylonitrile and, especially, of propane to acrylonitrile.

Because of the price differential between propylene and propane aneconomic incentive exists for the development of a viable catalyticprocess for conversion of propane to acrylonitrile.

Earlier attempts in the prior art to develop an efficient process forthe ammoxidation of propane to acrylonitrile produced eitherinsufficient yields or processes that necessitated adding halogenpromoters to the feed. The latter procedure would require not onlyreactors made of special corrosion resistant materials, but also thequantitative recovery of the promoter. The added costs thus eliminatedthe advantage of the propane/propylene price differential.

It is thus an object of the present invention to provide an improvedprocess for the ammoxidation of paraffins to unsaturated nitriles.

It is a further object of the invention to provide new catalyst systemsfor such process.

Still another object is to provide an improved catalytic ammoxidationprocess for making unsaturated nitriles from lower paraffins without theuse of halogen promoters.

Other objects, as well as aspects, features and advantages, of thepresent invention will become apparent from a study of the accompanyingdisclosure and the claims.

The foregoing and other objects of the present invention are achieved bythe process of the present invention. There are two main features of thepresent process invention. The first of these is the use of an excess ofthe alkane feed with relation to NH₃ and molecular oxygen. The secondfeature, which is used in combination with the high ratio of the C₃ toC₅ paraffin to NH₃ and O₂, is that a combination, i.e., a mixture, ofcatalysts is employed, the first catalyst composition being especiallyeffective to promote formation of an unsaturated nitrile and an olefinfrom the paraffin, and the second catalyst composition being especiallyeffective to promote the conversion of the olefin to the unsaturatednitrile. Such mixture is the subject of the composition claims herein.

In the present application "paraffin" designates an acyclic paraffin.

British Patent Specification Nos. 1,336,135 and 1,336,136 disclose theuse of high ratios of propane or isobutane to ammonia and oxygen, butonly single ammoxidation catalysts are used, and the yields ofacrylonitrile are extremely poor. U.S. Pat. No. 3,860,534 also disclosesuse of such high ratios, using a catalyst containing only V and Sboxides. However, after the catalyst is calcined, it is washed for 24hours with water and dried, a laborious procedure. A. N. Shatalova etal. in Neftekhiniya 8, No. 4, 609-612 (1968), describe the reaction ofpropane with oxygen and ammonia using a large excess of propane and amixture of two catalysts, one of which is described as oxides of metalshaving dehydrogenating characteristics at 550 and 600oC. At 500oC littleor no acrylonitrile was produced. Rather large amounts of propionitrileand acrolein were made per mole of acrylonitrile produced. The per passconversion of propane to acrylonitrile was generally 2-4 percent withselectivity to acrylonitrile being from 12 to 33 percent.

In the present process when applied to propane ammoxidation a smallamount of propylene is produced in relation to the unreacted propane inthe effluent. Such propane effluent containing propylene in the amountof up to 8 mole percent, but usually no more than 6 mole percent, of theamount of propane plus propylene can comprise the substrate feed to thepresent process. And in general the C₃ to C₅ alkane feed to the processcan contain one or more C₃ to C₅ olefins. The C₃ to C₅ olefin content ofthe feed to the present ammoxidation process can contain from zero to 8mole percent of such olefin(s), based on the moles of C₃ to C₅ paraffinplus olefins fed, and this feed can be from any source. Although largeramounts of C₃ to C₅ olefins may be present in the substrate paraffinfeed, usual amounts are as stated, and the usual olefin is thatcorresponding to the particular paraffin fed to the reaction zone of thepresent process.

According to the present invention there is provided a process for theammoxidation of a C₃ to C₅ paraffin which comprises contacting in areaction zone said paraffin in the vapor phase in admixture withammonia, molecular oxygen, and optionally an inert gaseous diluent, withan intimate particulate mixture of a first catalyst composition and asecond catalyst composition, said feed to the reaction zone containing amole ratio of paraffin:NH₃ in the range from 2 to 16 (usually 3-7), anda mole ratio of paraffin to 02 in the range from 1 to 10 (usually1.5-5), said first catalyst composition being 10-99 weight percent of adiluent/support and 90-1 weight percent of a catalyst having thecomponents in the proportions indicated by the empirical formula:

    VSb.sub.m A.sub.a B.sub.b C.sub.c T.sub.t O.sub.x,         formula (1)

where

A is one or more of W, Sn, Mo, B, P and Ge;

B is one or more of Fe, Co, Ni, Cr, Pb, Mn, Zn, Se, Te, Ga, In and As;

C is one or more of an alkali metal and Tl;

T is one or more of Ca, Sr and Ba; and

where m is from 0.01 and up to 20; a is 0.2-10; b is 0-20; c is 0-20(usually 0-1); t is 0-20; the ratio (a+b+c+t):(1+m) is 0.01-6; wherein xis determined by the oxidation state of the other elements, and whereinthe antimony has an average valency higher than +3 and the vanadium hasan average valency lower than +5, said second catalyst composition being0-99 weight percent of a diluent/support and 100-1 weight percent of acatalyst having the components in the proportions indicated by theempirical formula:

    A.sub.a C.sub.c G.sub.g Sn.sub.d Sb.sub.e O.sub.x          formula ( 2)

where

A is one or more of Cu, V, W, Mo

C is one or more of Bi, Ti, Ge, La, Ce, Cr, Mn, Mg Ca, Co, Ni, Pb, Nb,Ta, Zr, Ag, Zn, Cd, B, P, Ga, In, Te, Fe, Sm

G is one or more of K, Cs and Na

a is 0-10

c is 0-10

d is 0.1-10

e is 0.1-10

g is 0-1

(d+e) is 5-20

x is a number determined by the requirements of the other elementspresent, and

wherein the atoms of V:e is <0.01, the atoms of V:d is <0.01, the atomsof Fe are either less than d or are less than e, and wherein the weightratio in said mixture of said first catalyst composition to said secondcatalyst composition is in the range of 0.001 to 2.5.

In an especially useful catalyst of formula (1), m is greater than 1(often 2-10, more often 3-7).

By "particulate mixture" as used herein is meant a mixture of solidparticles or subdivided pieces of the first catalyst composition withseparate and distinct solid particles of the second catalystcomposition. The particles are often of a size used in fluidized bedreactors, say about 40 to 90 microns, but of course larger particles ofcatalyst can be employed for use in fixed or gravity flowing catalystbeds.

In the present process inaall its embodiments the ratio of O₂ to NH₃ fedto the reaction zone is usually in the range from 1 to 10 (more often1-5) and the ratio of inert gaseous diluent to paraffin is usually inthe range zero to 5 (more often zero to 3).

The diluent or support for either catalyst composition is a refractorymetal oxide or mixture, such as silica, silicaalumina, etc.

In the usual practice of the present invention the catalystsupport/diluent for the catalyst of formula (1) is not an oxide of anelement named in formula (1). Further, in the usual practice of theinvention the catalyst support/diluent for the catalyst of formula (2)is not an oxide of an element named in formula (2).

In the catalyst compositions of the invention the catalyst empiricalformulas (1) and (2) do not, of course, connote any particular chemicalcompound, nor indicate whether the elements are present as a mixture ofindividual oxides or as a complex oxide or oxides, or what separatecrystalline phases or solid solutions may be present. Similarly, thedesignation of certain oxides, such as "silica" or "alumina" or SiO₂ orAl₂ O₃, as supports or diluents is merely in accordance with conventionin the inorganic oxide catalyst art, and such designations refer tocompounds often regarded as supports in the catalyst art. Suchdesignations, however, do not mean that the element involved is actuallypresent as a simple oxide. Indeed, such elements may at times be presentas a complex oxide with one, more than one, or all of the elements informula (1) or formula (2), which complex oxides form during theprecipitation or agglomeration, drying and calcining process forpreparing the catalyst composition.

The process of the invention is especially useful in the ammoxidation ofpropane or isobutane.

According to the present invention the foregoing first catalystcomposition is prepared under conditions such that in the finalcomposition the average oxidation state of vanadium is less than 5.

One method for preparing the first catalyst composition is by a redoxreaction between a compound of trivalent antimony such as Sb203 and acompound of pentavalent vanadium such as V205, during which the antimonyis oxidized and the vanadium reduced.

The foregoing redox reaction was described by Birchall and Sleight(Inorganic Chem. 15, 868-70 [1976]) and by Berry et al. (J. Chem. Soc.Dalton Trans., 1983, 9-12), who effected the reaction by heating a drymixture of the above reactants at temperatures above 600° C. Thisproduct had a tetragonal rutiletype crystalline structure with a uniquex-ray diffraction pattern.

However, it has been found that the redox reaction can successfully andmore conveniently be carried out in an aqueous medium by heating at atemperature of at least 80° C. and up to 200° C., for instance, byheating an aqueous dispersion of a V⁵⁺ compound, such as NH₄ VO₃ or V₂O₅, with an Sb³⁺ compound, such as by reacting Sb₂ O₃ and NH₄ VO₃ (or V₂O₅). This step is followed by evaporation, drying and then calcining theproduct in a molecular oxygen-containing atmosphere, such as air, atfrom 350° to 700° or 750° C., usually 400° to 650° C. The length of thecalcination period may range from 30 minutes to 12 hours, butsatisfactory catalyst compositions are usually obtained by calcinationat such temperatures for a period of from 1 to 5 hours.

At least part of any excess of trivalent antimony compound, such as Sb₂O₃, is usually oxidized to Sb₂ O₄ during the calcination in a molecularoxygen-containing atmosphere, such as air.

The ingredients of the first catalyst composition other than vanadiumand antimony (and of course part of the oxygen) suitably ca beincorporated after completion of the foregoing redox reaction. Thus, theadditives A, B, C and/or T, if any, can be added in the slurry after theredox reaction, or the solid particles containing the vanadium andantimony values after separation from the aqueous medium can be coatedor impregnated in a known manner with such additives at any suitablestage prior to final calcination of the catalyst, by methods generallyknown in the art, using oxides, hydroxides, acids, salts (particularlyorganic salts such as acetates), and other compounds of such elements.

In formula (1) subscript a usually is at least 0.4 or 0.5. In formula(1) at least 0.2 atoms of W are usually present per atom of V, and thetotal of W plus Sn atoms ( if any Sn is present) is usually at least 0.4atoms. Preferred compositions of formula (1) contain at least 0.4 atomsof W per atom of V. Particularly when W is present, it is especiallyuseful to have at least 0.4 atoms of P per atom of V in addition to theW. Especially useful are such compositions wherein said diluent/supportcomprises 20-100 weight percent alumina and 80 to zero weight percentsilica.

Especially useful catalysts of formula (1) description are those inwhich a is at least 1, wherein A includes at least 1 atom of W.

Not only does the catalyst support in the first catalyst composition(formula (1)) improve mechanical stability of the catalyst, but also thecatalytic activity is significantly improved, especially in the case ofalumina and silica-alumina. Besides alumina and silica-alumina othersupports that can be used are silica, titania, silica-titania, Nb₂ O₅,silica-niobia, silicazirconia, zirconia and magnesia, etc.

In the first catalyst composition, now preferred support materials fornot only improving mechanical stability but also for improving the yieldof the desired nitriles are selected from silica-alumina and aluminahaving 20-100, usually 50-100, preferably 60-100 weight percent alumina;silica-titania and titania having 20-100 weight percent titania;silica-zirconia and zirconia having 80-100 weight percent zirconia; andsilica-niobia and niobia having 30-100 weight percent niobia (Nb₂ O₅).

In the preparation of the second catalyst composition of formula (2) themetal oxides can be blended together or can be formed separately andthen blended or formed separately or together in situ. Promoter oxides,if any, are preferably incorporated into the tin-antimony based catalystby blending into the gel before calcining or by blending into theoven-dried base catalyst before calcining. A preferred manne ofincorporating promoter elements is by choosing a water-soluble salt ofthe promoter element, forming an aqueous solution of the salt, andmixing the solution with a solution or a suspension of the base elementsor salts thereof. Optionally, the promoter elements can be incorporatedby the use of soluble complex salts or compounds with the desired baseelements which upon calcination will yield the desired ratio of theelements in the finished catalyst.

To introduce the tin component into the catalyst one may convenientlyuse an SnO₂ sol. Antimony is suitably introduced as Sb₂ O₃, or an Sb₂ O₅sol can be used. It is also possible to add finely divided antimonymetal to concentrated nitric acid and then to boil the slurry todecompose the excess nitric acid, leaving an antimony oxide slurry.

Other variations in starting materials will suggest themselves to oneskilled in the art, particularly when the preferred starting materialsmentioned hereinabove are unsuited to the economics of large-scalemanufacture. In general, any compounds containing the desired catalystcomponents may be used provided that they result, upon heating to atemperature within the range disclosed hereinafter, in the oxides of theinstant catalyst.

These second catalyst compositions are conveniently prepared by slurrytechniques wherein an aqueous slurry containing all of the elements inthe objective catalyst is produced, the water removed from the aqueousslurry to form a precatalyst precipitate or powder and the precatalystthen heated in the presence of an oxygen-containing gas such as air atelevated temperature to calcine the precatalyst thereby forming thecatalyst. Liquids other than water, such as C₁ to C₈ alcohols can alsobe used to form the precatalyst slurry.

In the second catalyst composition the support can be any of the usualsupports such as silica, alumina or silica-alumina, and the like.

In the ammoxidation of the present invention, the reaction is carriedout in the gas phase by contacting a mixture of the paraffin, ammoniaand molecular oxygen, and inert diluent, if any, conveniently in a fixedbed of the catalyst mixture, or a gravity flowing bed, a fluidized bedor a fast transport reactor mode.

Examples of inert diluents useful in the reaction are N₂, He, CO₂, H₂ Oand Ar.

The reaction temperature range can vary from 350° to 700° C., but isusually 430° to 520° C. The latter temperature range is especiallyuseful in the case of propane ammoxidation to acrylonitrile.

The average contact time can often be from 0 01 to 10 seconds, but isusually from 0.02 to 10 seconds, more usually from 0.1 to 5 seconds.

The pressure of the reaction usually ranges from 2 to 55 psia. Mostoften, pressure is somewhat above atmospheric.

The following examples of the invention are exemplary and should not betaken as in any way limiting.

EXAMPLE 1

A catalyst having the composition 60 wt % Cr₂ Cu₃.8 Te₁.7 W₀.2 Mo₀.5Sn₃₀ Sb₁₈ Cs₀.05 B₀.50 O_(x) -40 wt % SiO₂ was made as follows:

91 g of a 12 wt % Sb₂ O₅ sol was added to 208.2g of a 40 wt SiO₂ sol; 91g of the Sb₂ O₅ sol was added to 376.8g of an 18 wt % SnO₂ sol withheating and the two mixtures were combined. 12.01 g of Cr(NO₃)₃.9H₂ O,13.26 g of Cu(NO₃)₂.2.5 H₂ O and 1.46 g of a 10 wt CsNO₃ solution wereadded to another 121 g of the Sb₂ O₅ sol, and the pH was adjusted toabout 6 and the mixture stirred. This latter mixture was then added tothe Sn/Sb/Si mixture.

0.82 g ammonium metatungstate (85% WO₃ equivalent) and 1.32 g of (NH₄)₆Mo₇ O₂₄.4H₂ O were dissolved in water and then some of the total of 3.25g of Te metal to be added was introduced with about 12 ml of H₂ O₂. Then12 ml more of H₂ O₂ were added, and then the balance of the 3.25 g of Temetal was added. The mixture began to bubble, producing a clear yellowsolution. This was added to the above mixture, together with 0.46 g ofH₃ BO₃ and 61 g of a 12 wt % Sb₂ O₅ sol. The mixture was then digestedwith heating and stirring. Its pH was about 7.5. The mixture wasevaporated to dryness, heated at 290° C. for 3 hours, 425° C. for 3hours, ground and screened to 20/35 mesh and then heated 875 ° C. for 3hours.

EXAMPLE 2

A catalyst having the composition SbSn₃ Ti₀.4 O_(x) was made as follows:

388.92 gms. of an 18% SnO₂ sol was added to 208.73 gms of a 12% Sb₂ O₅sol with stirring. Then 21.08 gms of tetrabutoxytitanium was added andthe mixture was stirred and heated until it became thick. It was driedin an oven at 130° C. overnight, then heated 3 hours at 290° C., 3 hoursat 425° C., ground and screened to 20-35 mesh and heated 3 hours at 610°C.

EXAMPLE 3

A catalyst having the composition 60 wt % Cr₀.5 Cu₃.8 Te₁.7 W₀.7 Sn₃₀Sb₁₈ O_(x) -40 wt % SiO₂ was made.

2.86 g of ammonium metatungstate (85 wt % WO₃ equivalent) was dissolvedin about 25 ml of H₂ O. Then some of the 3.25 g Te metal ultimately tobe used was added to the tungsten solution with heating and stirring.Then a total of 50 ml H₂ O₂ was added in 10 ml aliquots until bubblingwas observed. Then the remainder of the 3.25 g Te metal was added insmall increments with continued bubling until the solution turned clear.

376.8 g of an 18 wt % SnO₂ was added to 364.0 g of a 12 wt % Sb₂ O₅ solin a beaker, and then 216.15 g of a 40 wt % SiO₂ sol was added to thebeaker. To this was then added the previously prepared clear solutioncontaining the Te and W values.

12.01 g of Cr(NO₃)₃.9H₂ O was dissolved in about 20 ml H₂ O, and 13.26 gof Cu(NO₃)₂.2.5 H₂ O was added to about 30 ml H₂ O. The Cr and Cudispersions were then combined and then slowly added to the beaker withadditional water. The total volume was about 1900 ml. The pH of theresulting slurry was about 5.5. The slurry was evaporated to dryness,and the solid heated for 3 hours at 290° C. and for 3 hours 425° C., theground to 20-35 mesh, and finally calcined by heated for 3 hours at 875°C.

EXAMPLE 4

A catalyst having the empirical formula 50 wt % VSb₃.5 P₀.5 WO_(x) +50wt % Al₂ O₃ support was made as follows:

In a stirred flask equipped for heating under reflux, 3.81 g NH₄ VO₃were dissolved in 90ml hot water. To the hot solution 16.6 g Sb₂ O₃ wereadded, and the slurry was boiled under reflux for 16-18 hours overnight.There was ammonia evolution, and the vanadium antimony mixture turnedgray-green.

In a separate operation, 35.3 g Catapal SB (hydrated alumina) were mixedwith 127.2 ml H₂ O (cold)+14.1 g acetic acid (10 percent solution) andstirred until the suspension gelled. It took about 3 hours, and the gelwas soft, homogeneous, with the consistency of thick cream.

Meanwhile, the vanadium antimony slurry was transferred to a beaker. Asolution of 8.80 g ammonium meta-tungstate in about 20 ml H₂ O and asolution of 1.77 g (NH₄)₂ HPO₄ in H₂ O were then added, followed by theaddition, with stirring (magnet) of the alumina gel. After partialevaporation, the mixture became too thick for stirring. It was thentransferred to an evaporating dish, and the evaporation, following bydrying overnight, was continued in an oven at 110°-120° C. The driedmaterial was precalcined at 350° C. for 5 hours, screened to 20/35 mesh,then calcined 3 hours at 610° C.

EXAMPLE 5

A catalyst having the empirical formula 45 wt % VSb₃.5 P₀.5 WO_(x) +55wt % Al₂ O₃ support was made as follows:

In a stirred flask, 7.07 g of ammonium metatungstate and 3.03 g NH₄ VO₃were dissolved in 200ml hot water, and 1.49 g of 85% H₃ PO₄ was added.To the hot solution 13.22 g Sb₂ O₃ were added, and the slurry wasstirred and heated for about 1 hour.

In a separate operation, 32.35 g Catapal SB (hydrated alumina) weremixed with 120 ml H₂ O (cold)+5.5 g acetic acid (10 percent solution)and stirred for 1 hour. The resulting dispersion was added to the othermixture with stirring. The resulting slurry was partially evaporated ona hotplate, followed by drying overnight in an oven at 110°-120° C. Thedried material was precalcined at 350° C. for 5 hours, screened to 20/35mesh, then calcined 3 hours at 610° C.

In the ammoxidation runs of the following examples, the catalyst, or themixture of catalysts, is in a tubular 3/8 inch I.D. stainless steelfixed bed reactor. When a mixture of particulate catalysts is used, asin the invention examples, the desired weight of each of the twocatalyst compositions is put in a vial and shaken until uniformlydispersed before placing the desired amount of the catalyst mixture inthe reaction tube. The reaction is equipped with a preheat leg and isimmersed in a temperature controlled molten salt bath. The gaseous feedcomponents are metered through mass flow controllers into the bottom ofthe reactor through the preheat leg. Water is introduced through aseptum at the top of the preheat leg, using a syringe pump. The feed isfed to the catalyst for 1 hour before collection of product; the runs ofeach example last 30-60 minutes during which the product is collectedfor analysis.

EXAMPLE 6

In this example the catalyst was a mixture of the catalyst of Example 2and the catalyst of Example 4 in the weight ratio of the latter to theformer of 0.15. The reaction temperature was 470° C. and the molar feedratios were 5 propane/1 NH₃ /2 O₂ /1 H₂ O. The contact time was 0.8seconds. Analysis of the reactor effluent showed that propane conversionwas 13.1 percent; yield and selectivity of propane to acrylonitrile were5.9 and 44.8 percent, respectively; selectivity to propylene was 22.7percent; selectivity to HCN was 8.9 percent.

COMPARATIVE EXAMPLE A

In this example the reaction temperature was 470° C. and the molar feedratios were 5 propane/1 NH₃ /2 O₂ /1 H₂ O. The catalyst was the catalystof Example 2 alone. The contact time was 0.5 seconds. Analysis of thereactor effluent showed that propane conversion was only 3.0 percent;yield and selectivity of propane to acrylonitrile were 1.3 and 42.2percent respectively; selectivity to propylene was 15.9 percent;selectivity to HCN was 16.6 percent.

EXAMPLE 7

In this example the catalyst was a mixture of the catalyst of Example 2and the catalyst of Example 5 in the weight ratio of the later to theformer of 0.105. The reaction temperature was 470° C. and the molar feedratios were 5 propane/1 NH₃ /2 O₂ /1 H₂ O. The contact time was 1.2seconds. Analysis of the reactor effluent showed that propane conversionwas 13.5 percent; yield and selectivity of propane to acrylonitrile were5.8 and 43.0 percent, respectively; selectivity to propylene was 15.8percent; selectivity to HCN was 7.8 percent.

EXAMPLE 8

In this example the catalyst was a mixture of the catalyst of Example 1and the catalyst of Example 4 in the weight ratio of the latter to theformer of 0.15. The reaction temperature was 470° C. and the molar feedratios were 5 propane/1 NH₃ /2 O₂ /1 H₂ O. The contact time was 1.6seconds. Analysis of the reactor effluent showed that propane conversionwas 12.4 percent; yield and selectivity of propane to acrylonitrile were4.9 and 39.4 percent, respectively; selectivity to propylene was 31.8percent; selectivity to HCN was 5.4 percent.

EXAMPLE 9

In this example the catalyst was a mixture of the catalyst of Example 3and the catalyst of Example 4 in the weight ratio of the latter to theformer of 0.15. The reaction temperature was 470° C. and the molar feedratios were 5 propane/1 NH₃ /2 O₂ /1 H₂ O. The contact time was 1.5seconds. Analysis of the reactor effluent showed that propane conversionwas 12.2 percent; yield and selectivity of propane to acrylonitrile were4.0 and 33.0 percent, respectively; selectivity to propylene was 37.3percent; selectivity to HCN was 8.4 percent.

EXAMPLE 10

In this example the catalyst was a mixture of the catalyst of Example 1and the catalyst of Example 4 in the weight ratio of the latter to theformer of 0.15. The reaction temperature was 470° C. and the molar feedratios were 5 propane/1 NH₃ /2 O₂ /1 H₂ O. The contact time was 1.6seconds. Analysis of the reactor effluent after a pre-run of 24 hoursshowed that propane conversion was 10.1 percent; yield and selectivityof propane to acrylonitrile were 3.9 and 38.7 percent, respectively;selectivity to propylene was 35.1 percent; selectivity to HCN was 8.4percent.

EXAMPLE 11

In this example the catalyst was a mixture of the catalyst of Example 2and the catalyst of Example 4 in the weight ratio of the latter to theformer of 0.15. The reaction temperature was 470° C. and the molar feedratios were 5 propane/1 NH₃ /2 O₂ /1 H₂ O. The contact time was 1.5seconds. Analysis of the reactor effluent after a pre-run of 24 hoursshowed that propane conversion was 9.2 percent; yield and selectivity ofpropane to acrylonitrile were 2.9 and 31.6 percent, respectively;selectivity to propylene was 40.7 percent; selectivity to HCN was 10.0percent.

As will be evident to those skilled in the art various modifications ofthis invention can be made or followed in the light of the foregoingdisclosure and discussion without departing from the spirit and scope ofthe disclosure or from the scope of the claims.

We claim:
 1. A catalytic mixture suitable for the ammoxidation ofpropane to acrylonitrile, which comprises an intimate particulatemixture of a first catalyst composition and a second catalystcomposition, said first catalyst composition being 10-99 weight percentof a diluent/support and 90-1 weight percent of a catalyst having thecomponents in the proportions indicated by the empirical formula:

    VSb.sub.m A.sub.a B.sub.b C.sub.c T.sub.t O.sub.x,         formula (1)

where A is one or more of W, Sn, Mo, B, P and Ge and includes at least0.2 atoms of W per atom of V; B is one or more of Fe, Co, Ni, Cr, Pb,Mn, Zn, Se, Te, Ga, In and As; C is one or more of an alkali metal andTl; T is one or more of Ca, Sr and Ba; andwhere m is from 0.01 and up to20; a is 0.2-10; b is 0-20; c is 0-1; t is 0-20; the ratio(a+b+c+t):(1+m) is 0.01-6; wherein x is determined by the oxidationstate of other elements, and wherein the antimony has an average valencyhigher than +3 and the vanadium has an average valency lower than +5,said second catalyst composition being 0-99 weight percent of adiluent/support and 100-1 weight percent of a catalyst having thecomponents in the proportions indicated by the empirical formula:

    A.sub.a C.sub.c G.sub.g Sn.sub.d Sb.sub.e O.sub.x          formula ( 2)

where A is one or more of Cu, V, W, Mo C is one or more of Bi, Ti, Ge,La, Ce, Cr, Mn, Mg Ca, Co, Ni, Pb, Nb, Ta, Zr, Ag, Zn, Cd, B, P, Ga, In,Te, Fe, Sm G is one or more of K, Cs and Na a is 0-10 c is 0-10 d is0.1-10 e is 0.1-10 g is 0-1 (d+e) is 5-20 x is a number determined bythe requirements of the other elements present, andwherein the atoms ofV:e is <0.01, the atoms of V:d is <0.01, the atoms of Fe are either lessthan d or are less than e, and wherein the weight ratio in said mixtureof said first catalyst composition to said second catalyst compositionis in the range of 0.001 to 2.5.
 2. A mixture of claim 1 wherein A ofthe formula (1) includes at least 0.2 atoms of W per atom of V and thetotal A atoms include at least 0.4 (W atoms+Sn atoms) per atom of V. 3.A mixture of claim 1 wherein A of formula (1) includes at least 0.4atoms of P per atom of V.
 4. A mixture of claim 1 wherein said supportfor the catalyst of formula (1) is selected from silica, alumina,titania, silica-niobia, silica-zirconia, silica-titania, silica-alumina,Nb₂ O₅ and magnesia.
 5. A mixture of claim 2 wherein said support forthe catalyst of formula (1) is selected from silica-alumina and aluminahaving 20-100 weight percent alumina; silica-titania and titania having20-100 weight percent titania; silica-zirconia and zirconia having80-100 weight percent zirconia; and silica-niobia and niobia having30-100 weight percent niobia (Nb₂ O₅).
 6. A mixture of claim 2 wherein mis 2-10.
 7. A mixture of claim 3 wherein m is 2-10.
 8. A mixture of anyone of claims 2 or 3 wherein said diluent/support in said first catalystcomposition comprises 20weight percent alumina and 80 to zero weightpercent silica.
 9. A mixture of claim 2 wherein said diluent/support insaid first catalyst composition comprises 50-100 weight percent aluminaand 50 to zero weight percent silica.